1. Field of the Invention
The present invention relates to a spread illuminating apparatus used as an illumination means of a liquid crystal display device or the like.
2. Description of the Related Art
Currently, a liquid crystal display device is generally used as a display device of electronic devices such as personal computers and mobile telephones. Since liquid crystal is not a self-emitting display element, in a transmissive liquid crystal display device, for example, an illumination means that illuminates light on the liquid crystal panel is essential. Even in a semi-transmissive liquid crystal display device that uses external light, an auxiliary illumination means is provided to enable the device to be used in dark places. As such an illumination means for a liquid crystal display device, a spread illuminating apparatus that includes a light guide plate and a light source disposed on the side of the light guide plate as main constituent components is widely used in combination with liquid crystal display devices because it is advantageous that it is easy to be made thin. Further, a spread illuminating apparatus using a white LED as the light source has become common in accordance with recent technological advances in white light emitting diodes (LEDs) in order to make such spread illuminating apparatuses even more compact, thin and less power.
FIG. 6 illustrates one example of a display device equipped with such a spread illuminating apparatus. In FIG. 6, a display device 100 includes a plurality of plate-shaped (or sheet-shaped) members such as a liquid crystal display panel (LCD) 110 including a pair of glass substrates 112 and a pair of polarizing plates 114, a light guide plate 116 disposed on an underside surface side of the LCD 110 and where one (a top surface) of a pair of opposing principal surfaces is a light emitting surface, a reflective sheet 118 disposed on an underside surface side of the light guide plate 116, and a multi-layered (4 layers in the example of FIG. 6) optical sheet 120 disposed between the LCD 110 and the light guide plate 116 as constituent components. The above-described constituent components are accommodated together with a point light source 122 such as a white LED disposed facing an incident light surface 116a (FIG. 6C) of the light guide plate 116 in a frame-shaped inside part of a frame 124 made of synthetic resin material so as to constitute the integrated display device 100.
In the display device 100 having the above-described structure, the LCD 110 is fixed via two-sided tape 126 (FIG. 6B) to an attachment seat 124a that is formed to protrude toward the inside of the frame 124. The optical sheet 120 includes, for example, a diffusion sheet, a prism sheet, or the like, and is fixed via the two-sided tape 126 to the attachment seat 124a of the frame 124 similar to the LCD 110. Further, the reflective sheet 118 is also fixed via a two-sided tape 127 to an attachment seat 124b that is formed to protrude toward the inside of the frame 124. In addition, a light-blocking member 128 that covers the point light source 122 and the incident light surface 116a of the light guide plate 116 (FIG. 6C) is provided. Reference numeral 130 in FIG. 6C indicates a two-sided tape, and reference numeral 132 indicates a wiring substrate of the point light source (for example, refer to Japanese Patent Application Laid-Open No. 2010-224000).
In order to ensure accurate positioning of the optical sheet 120, a tab 120a as shown in FIG. 5A is formed on an edge of the optical sheet 120, and a recessed part 124c having a complementary shape for accepting the tab 120a is formed at a corresponding position on the frame 124. Therefore, as shown in FIG. 5A, positioning of the optical sheet 120 on the frame 124 is performed in the directions of arrows A and B which are orthogonal to each other (for example, refer to Japanese Patent Application Laid-Open No. 2009-265237 and Japanese Patent Application Laid-Open No. 2006-154320).
As explained above, the display device 100 has a structure where the necessary constituent parts are retained integrally and the necessary strength is secured by the frame 124 that is disposed surrounding the LCD 110 like a frame. Therein, from the perspective of the functionality of downsizing the display device 100 as well as the perspective of the design of the display device 100, there is a constant demand to narrow the frame of the display device 100. If the thickness (thickness in the direction of arrows B in FIG. 5A) of the frame 124 is reduced in order to facilitate this narrowing of the frame, it becomes difficult to secure the recessed part 124c for accepting the tab 120a of the optical sheet 120. Since the positioning of the optical sheet 120 may thereby become insufficient, this presents an obstacle to satisfying the demand to narrow the frame of the display device 100. Further, the tab 120a of the optical sheet 120 may also become a factor leading to unevenness in the brightness of the spread illuminating apparatus that constitutes the display device 100.